Phototube



Aug. 23, 1938.

A. G. THOMAS Original Filed May 13, 1956 lnvenlor Patented Aug. 23, 1938UNITED STATES PATENT OFFICE Original application May 13, 1936, SerialNo. 79,420. Divided and this application April 24, 1937, Serial No.138,692

2 Claims. (01. 250-27.5)

This invention relates to photo-tubes for use in radio and in televisionand the like, and is a division from my co-pending application, SerialNo. 79,420, filed May 13, 1936.

An object is to provide a photo-tube in which electrons are liberated bysuccessive reflections from a photo-emissive surface or surfaces.

Another object is to provide a phototube with a light reflecting andphoto-sensitive cathode in combination with re-reflecting surfaces.

A further object is to provide a tube in which magnetic fields are usedin order to produce secondary emission.

Other objects will appear in the specification.

In the drawing:

The figure is an elevation in part section of a photo-tube employinglight reflections between photo-emissive surfaces, to increase theelectron output.

In the figure tube I has parallel plates 2 and 3 supported by metalprojections 9 and I sealed into tube I. Wedge-shaped cathode 4 issuitably supported in tube I and is coated with potassium hydride or acaesium compound or with any suit- I able substance that emits electronsunder infiuence of light. The inner surfaces of plates 2 and 3 aresimilarly coated. Anode plate 6 is connected to the positive terminal ofbattery I, the negative terminal being connected to cathode 4. Element 8may be included in the output circuit for any desired purpose. Lens isplaced so that it will gather a large amount of light and concentrate iton the inclined faces of cathode 4 so that a large number of electronswill be liberated from this cathode, since the number of electronsemitted is substantially proportional to the intensity of the lightstriking the cathode.

Cathode 4 is also smoothly coated so that it will readily reflect lightso that the light rays will be reflected from the inclined faces ofwedge-shaped cathode 4 and thence back and forth from plate- 2 to 3 andvice versa, each reflection producing additional electrons so that alarge number of electrons will finally reach positively charged plate 6.Plates 2 and 3 may be grounded by wires I1 and I8 if desired and chargedscreens similar to those of Figure 3 as illustrated in my parentapplication, Serial No. 79,420, filed May 13, 1936, 5 may be employed.These screens themselves may be coated with substances suitable foremitting secondary electrons by electronic bombardment or by the actionof light.

A series of alternately oppositely disposed mag- 10 netic fields I4, I5and I6 produced by magnets I I, I2 and I3 respectively may be used withtube I so that the electrons will be deflected back and forth betweenplates 2 and 3 as well as light, with the result that secondaryelectrons will be produced by electronic bombardment also. The addedeffects of the reflected and re-reflected light and the electronicbombardment of plates 2 and 3 will cause a very high output currentthrough element 8. Magnets II, I2 and I3 may be omitted however. Plates2 and 3 may be grounded to prevent the accumulation of positive chargeson them or they may be connected to cathode 4 through a high resistance.Mirrors may be used to collect light instead of lens 5. Cathode 4 may bea cone, and plates 2 and 3 may be replaced by a cylinder with coatedinner surface.

What I claim is:

1. A phototube comprising, a light reflecting photo-sensitive cathode,an anode, and a pair of opposed photo-sensitive surfaces adapted torefiect light from said cathode from one said surface to the other saidsurface to liberate electrons from said surfaces.

2. A phototube comprising, a light reflecting photo-sensitive cathode,an anode, and photosensitive light-reflecting means disposed betweensaid cathode and said anode and adapted to cause repeated reflectionsupon said means of light from said cathode to liberate electrons fromsaid means.

ALBERT G. THOMAS.

